The invention concerns a steering arrangement for a vehicle, in particular for an automotive machine, with a steering drive controlled by a steering unit.
In automotive machines, for example fork lift trucks, used in warehouses, a relatively large number of steering operations must be performed in the course of a working day or a work shift, during which steering operations the driver or the operating person effects a change of direction by operating a steering handwheel. The steering handwheel can act directly or indirectly upon the steering drive, for example a hydraulic motor.
To ease the work for the operating person, the steering handwheels known from normal motor cars have earlier been replaced by the so-called xe2x80x9cmini steering wheelsxe2x80x9d. This change was based on considerations about the fact that it would save force for the operating person, if the steering movement could be performed by means of one hand, and substantially by the forearm area and the hand. Because of the reduced size of the mini steering wheel the required movement is substantially shorter.
However, it has turned out that also the mini steering wheel only offers a limited improvement of the working conditions. The force to be used by the operating person for the movements is in fact reduced. However, when the number of movements exceeds 10 to 20 times per minute, elbows and forearms are increasingly exposed to injuries. But a normal working day with fork lift trucks cannot be managed with less movements.
The purpose of the invention is to design a steering, which is less straining for the operator.
In a steering arrangement of the kind mentioned in the introduction, this task is solved in that the steering unit has a keyboard instead of a steering handwheel.
The operation of a keyboard normally only requires moving the fingers. During this operation, forearm and elbow can rest. It has been established that only 10 to 20 movements of elbow and forearm are allowed per minute, to avoid the risk of damage. However, fingers can perform up to 200 movements per minute without showing signs of damage. When considering that, for example with fork lift trucks in warehouses, the typical movement pattern comprises that the driver picks up, ranges and puts down a palette, often requiring direction changes of the fork lift truck by approximately 90xc2x0, which means three to five rotations of the mini steering handwheel, it can be imagined that the replacement of the steering handwheel by a keyboard does not reduce the number of required movements, however, it means that the movements are performed by the fingers, not by the elbow and the forearm.
The use of keyboard-operated steering units in the vehicle field is known per se. U.S. Pat. No. 5,035,439 shows a steering unit, with which the rear wheels of an articulated vehicle trailer can be weight relieved and then deflected, to manage sharp bends. However, this steering unit is only used for special purposes. Otherwise, the tractor truck is steered by means of a normal steering handwheel.
EP 0 479 735 A2 shows an electric car, the tailgate of which is also provided with a keyboard, by means of which the vehicle can be moved by inching. Normally, the vehicle is steered by a steering handwheel, like a normal car.
However, in connection with parking, the driver can leave the vehicle, and park it in even narrow parking spaces by means of the additional keyboard on the back.
Preferably, the keyboard has at least two direction-determining keys. The operation of one key causes, for example, a deflection of the steering drive to the left. The other key causes a corresponding movement to the right. This is most similar to the feeling of a driver, so that also with regard to feeling the keyboard can replace the steering handwheel.
Preferably, the keyboard has resting keys, which need a predetermined force to be activated. There is no reason why the direction-determining keys should not also be the resting keys. They permit the driver or the operator to let his hand, or at least his finger, rest on the keys during normal driving, without risking an operation of the keys. The predetermined force required for the operation is thus larger than the weight force of the finger or the hand, respectively, of the operator. Only when the driver wants a direction change of the vehicle, he deliberately activates the key to initiate the corresponding steering movement. Thus, an activation of the key does no longer require a movement of the finger towards the keys. On the contrary, the finger can remain on site and rest. This additionally increases the comfort of the steering unit.
In an alternative or additional embodiment, the keyboard can have pressure-sensitive keys, whose output signal depends on the pressure acting upon them. For example, the output signal can be the more powerful, the more the keys are pressed. The more powerful the output signal is, the higher can, for example, the angle speed be, with which the steering drive moves the steered wheel.
In a preferred embodiment the keyboard has a dead man""s button. Such a dead man""s button must, for example, be activated by the driver from time to time, to show that the driver is still in control of the vehicle. When this activation does not occur, a warning signal sounds, and the vehicle is then inactivated, that is, the vehicle stands still. This is an additional security aspect, which is difficult to realise in connection with a steering handwheel, as normally the operator does not have a defined working point on the steering wheel.
Preferably, at least one key of the keyboard has a detection unit for at least one person-specific feature, particularly a finger-print. This does not only provide an antitheft. It also permits the direct insertion of certain driver or person dependent parameters in the steering unit, without requiring additional activities from the operator. The moment the detection unit recognises a certain operator, it can activate the programme stored for this certain operator. The most simple case could be a change from right-hand to left-hand operation or vice versa. However, it is also possible that each operator has a preferred driving pattern, which can be activated with simple key operating combinations, enabling a distinguishing between the individual driving patterns from person to person.
Preferably, the keyboard has a handhold area with a feedback device. The handhold area serves the purpose of supporting the hand of the operator. During operation, it must thus be assumed that the hand of the operator lies on or at the handhold area. When now the feedback device offers the opportunity of sending messages to the operator, a feedback acting upon the person can be provided here. For example, the feedback device can be used to inform the driver that the steered wheel has reached its end position or that the permissible steering speed has been exceeded, if required also in dependence on the vehicle speed.
In a particularly preferred embodiment it is provided that the feedback device has a vibration producing arrangement and/or an attemperation arrangement. A vibration producing arrangement makes the handhold area vibrate slightly, but enough to be felt by the driver. If required, the oscillation amplitude or the frequency can be changed, to indicate different hazard or limit situations. Also with the attemperation arrangement a similar signal can be achieved. When the handhold area is cooled or heated by a few degrees, the driver becomes a clear signal of a certain operating behaviour.
Preferably, the keyboard is arranged in a housing, which has a BUS-connection. In this case, control electronics can be provided in the housing, which plot the operation of the keys, and, if required, analyse and evaluate it. In this case, signals are transmitted to the steering drive via the BUS-arrangement, for example a CAN-BUS, said steering drive having a corresponding BUS-connection. When using a hydraulic steering drive, the BUS can also be used for direct activation of a proportional valve. On the other hand, the BUS can also serve the purpose of feedback and, for example, operate the feedback device.
In a preferred embodiment the keyboard is connected with a function generator, which, in dependence of a key operation, causes a time and/or movement dependent operation of the steering drive. In the most simple case, the steering drive is operated in one direction for as long as the corresponding direction key is pressed. When the key is released, the steered wheel remains in the desired position. By means of the function generator, however, the resetting can be simplified, in that the steered wheel is returned to the neutral or the straight ahead position, when both keys of the keyboard are pressed simultaneously. In this case it is even sufficient to press both keys simultaneously or almost simultaneously and then release them. Of course, it is also possible to hold both keys down simultaneously to bring the steered wheel back to the straight ahead position. When the wheel has reached the straight ahead position, the turning of the steered wheel will be interrupted, no matter if the keys are still pressed. It can also be provided that the steering speed is increased concurrently with the duration of the key pressing, or that the steering speed is high at the beginning and then reduced, or vice versa. The steering speed, that is, the speed of the angle movement of the steered wheel, can also be adapted to the speed and/or the load of the vehicle. For all these functions, the function generator is a valuable accessory.
It is particularly preferred that the function generator has an inlet with a time demodulator, which, on a key operation, opens a time window, in which an additional key operation causes a deviating deflection of the steering drive. A time demodulator increases the number of pieces of information, which can be transferred to the steering drive from the keyboard. This can, for example, be compared with the mouse of a personal computer (PC). On a computer mouse you can click once or twice, and this causes the PC to react differently. In the same way, double clicking of a direction key can cause that the wheel is steered to its end position in the corresponding direction, regardless of the initial position of the steered wheel. With a double clicking a xe2x80x9cprecision steeringxe2x80x9d can also be started, with which the steered wheel is moved at reduced steering speed. The double clicking can also cause the wheel to go to a different end position than a single clicking. Preferably, the reaction behaviour of the steering unit is programmable.